A need has long existed for a solid fuel composition that is:
(a) readily storable with long shelf life without special packaging or handling;
(b) readily ignitable when combustion is desired, yet resistant to ignition under normal shipping or storage conditions;
(c) capable upon combustion of generating a sufficiently hot flame temperature to provide useful quantities of heat--such as for cooking or other purposes; and
(d) capable of providing a long-lasting fuel source yet which is also compact and readily transportable.
The art discloses many efforts to develop a solid fuel source which embodies some or all of the above features. Thus, in connection with the problem of handling, transportation and storage, many efforts have been directed to the formulation of jellied gasoline or hydrocarbon fuels. For example, see U.S. Pat. Nos. 2,581,441; 2,610,113; 3,460,921; 3,718,445; 3,824,085 and 3,795,556. Solidified alcohol based fuels have also been disclosed. See U.S. Pat. Nos. 1,752,935; 3,754,877 and 3,964,880. Solid fuel formulations which in part comprise a copolymer formaldehyde resin, such as urea-formaldehyde or phenol-formaldehyde, have been disclosed. See. U.S. Pat. Nos. 3,615,286; 3,801,292; 4,001,152 and 4,083,697. Solid fuel compositions comprising polymers of formaldehyde, such as paraformaldehyde and linear hydrated formaldehyde polymers, and of acetaldehydes, such as paraldehyde and metaldehyde, have been suggested. See U.S. Pat. Nos. 1,407,101; 1,452,293; 1,895,955; 2,161,385 and 2,915,560. Paraformaldehyde resins are unsatisfactory in that they are water soluble, which presents storage problems, and emit the sharp odor of formaldehyde when combustion is extinguished. U.S. Pat. No. 2,915,560 discloses a process for producing a linear hydrated formaldehyde polymer, that in some respects appears to possess properties similar to those of acetal resins. It is stated that this material is compressible into dense hard fuel tablets which burn with a non-luminous flame that does not give off a detectable odor of formaldehyde.
However, it does not appear that any practical solid fuel composition employing a formaldehyde type resin--including acetal type resins--has yet been developed. This apparently stems from the fact that an acetal resin alone, although it is known to have clean-burning characteristics resulting in no smoke generation, nevertheless will not burn with sufficient heat liberation to be useful as a practical heat source for cooking or other like uses.
Acetals are slow burning resins. Their flame temperature is about 600.degree. F., which in itself may appear to be sufficient for cooking purposes until it is realized that the flame of the burning resin is extremely localized in nature. That is, the height to which the flame extends above the combustion surface is very small, thus the heat liberated by the flame is extremely localized. If the flame produced by combustion of a pure acetal resin is to be utilized, the item to be heated thereby must be brought into such close proximity to the combustion surface as to impede the free flow of oxygen across the combustion surface, thus producing a very unstable flame. If the item to be heated is held away from the combustion surface so as not to impede the flow of oxygen thereto, then any disturbance of the air between the combustion surface and the object would dissipate the upward flow of heat generated by the low temperature flame and would thereby preclude a useful quantity of heat from reaching the object to be heated.
Clearly, an acetal resin alone has not proven satisfactory as a solid fuel source for outdoor use.